1. Field of the Invention
The present invention relates to a anti-reducing dielectric ceramic composition and a monolithic ceramic capacitor using the dielectric ceramic composition.
2. Description of the Related Art
When a dielectric material mainly containing a titanate is used to form a monolithic ceramic capacitor, there has been the problem that when such a dielectric material is sintered under a condition of a low concentration oxygen partial pressure (neutral or reductive atmosphere), the dielectric material is undesirably reduced and hence undesirably becomes a semi-conductor. Because of this, in order to form internal electrodes, it is necessary to employ a noble metal such as palladium and platinum which will not melt under the sintering temperature, nor will it cause the dielectric ceramic material to be converted to a semi-conductor and itself be oxidized under a high concentration oxygen partial pressure. As a result, it is difficult to manufacture a monolithic ceramic capacitor with a low cost.
It is usually desired to use, as an internal electrode material, inexpensive base metals such as nickel and copper. However, when such a base metal is used as an internal electrode material and is sintered under conventional conditions, said electrode material is oxidized. As a result, it is impossible to provide the desired function of an electrode. For this reason, in order for such base metal to be used as an internal electrode material, it is necessary to employ a dielectric material having an excellent dielectric property with its ceramic layer having resistance against becoming a semiconductor even under a neutral or reductive atmosphere having a low concentration oxygen partial pressure. In order to meet such a requirement, Japanese laid-open patent application Nos. 63-289707 and 63-224106 suggest an improved dielectric material which is (Ca.sub.1-x Sr.sub.x) (Zr.sub.1-y Ti.sub.y)O.sub.3 composition. By using such improved dielectric material, it has become possible to obtain a dielectric ceramic which is not converted into a semiconductor even when being sintered in a reductive atmosphere, thereby rendering it possible to manufacture a monolithic ceramic capacitor using a base metal material such as nickel or copper for forming internal electrode.
With the anti-reducing dielectric ceramic composition disclosed in the above Japanese laid-open patent application No. 63-289707, there is a problem that although it has excellent capacity and temperature characteristics, its dielectric constant is as low as 46. With the anti-reducing dielectric ceramic composition disclosed in the above Japanese laid-open patent application No. 63-224106, there is a problem that if the thickness of laminated ceramic body is made quite thin for the purpose of producing a monolithic ceramic capacitor compact in size but large in capacity, it is difficult to ensure the desired reliability during a life measuring test under a high temperature load.